netfilter: add nf_ipv6_ops hook to fix xt_addrtype with IPv6

Quoting https://bugzilla.netfilter.org/show_bug.cgi?id=812:

[ ip6tables -m addrtype ]
When I tried to use in the nat/PREROUTING it messes up the
routing cache even if the rule didn't matched at all.
[..]
If I remove the --limit-iface-in from the non-working scenario, so just
use the -m addrtype --dst-type LOCAL it works!

This happens when LOCAL type matching is requested with --limit-iface-in,
and the default ipv6 route is via the interface the packet we test
arrived on.

Because xt_addrtype uses ip6_route_output, the ipv6 routing implementation
creates an unwanted cached entry, and the packet won't make it to the
real/expected destination.

Silently ignoring --limit-iface-in makes the routing work but it breaks
rule matching (--dst-type LOCAL with limit-iface-in is supposed to only
match if the dst address is configured on the incoming interface;
without --limit-iface-in it will match if the address is reachable
via lo).

The test should call ipv6_chk_addr() instead.  However, this would add
a link-time dependency on ipv6.

There are two possible solutions:

1) Revert the commit that moved ipt_addrtype to xt_addrtype,
   and put ipv6 specific code into ip6t_addrtype.
2) add new "nf_ipv6_ops" struct to register pointers to ipv6 functions.

While the former might seem preferable, Pablo pointed out that there
are more xt modules with link-time dependeny issues regarding ipv6,
so lets go for 2).

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 8 insertions, 1 deletions

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d1ab6ab29a55..d1b2d8034b54 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1487,7 +1487,7 @@ static int ipv6_count_addresses(struct inet6_dev *idev)
 }
 
 int ipv6_chk_addr(struct net *net, const struct in6_addr *addr,
-		  struct net_device *dev, int strict)
+		  const struct net_device *dev, int strict)
 {
 	struct inet6_ifaddr *ifp;
 	unsigned int hash = inet6_addr_hash(addr);
diff --git a/net/ipv6/netfilter.c b/net/ipv6/netfilter.c
index 72836f40b730..95f3f1da0d7f 100644
--- a/net/ipv6/netfilter.c
+++ b/net/ipv6/netfilter.c
@@ -10,6 +10,7 @@
 #include <linux/netfilter.h>
 #include <linux/netfilter_ipv6.h>
 #include <linux/export.h>
+#include <net/addrconf.h>
 #include <net/dst.h>
 #include <net/ipv6.h>
 #include <net/ip6_route.h>
@@ -186,6 +187,10 @@ static __sum16 nf_ip6_checksum_partial(struct sk_buff *skb, unsigned int hook,
 	return csum;
 };
 
+static const struct nf_ipv6_ops ipv6ops = {
+	.chk_addr	= ipv6_chk_addr,
+};
+
 static const struct nf_afinfo nf_ip6_afinfo = {
 	.family			= AF_INET6,
 	.checksum		= nf_ip6_checksum,
@@ -198,6 +203,7 @@ static const struct nf_afinfo nf_ip6_afinfo = {
 
 int __init ipv6_netfilter_init(void)
 {
+	RCU_INIT_POINTER(nf_ipv6_ops, &ipv6ops);
 	return nf_register_afinfo(&nf_ip6_afinfo);
 }
 
@@ -206,5 +212,6 @@ int __init ipv6_netfilter_init(void)
  */
 void ipv6_netfilter_fini(void)
 {
+	RCU_INIT_POINTER(nf_ipv6_ops, NULL);
 	nf_unregister_afinfo(&nf_ip6_afinfo);
 }